The invention relates to a grinding machine, such as a cam shaft grinding machine and an orbital pin grinding machine, or more particularly, a device for measuring a radius of grindstone in a grinding machine.
A grinding machine that numerically controls a feed shaft of a wheel spindle stock is known. In this grinding machine, a rotating grindstone moves in a feed direction of the feed shaft to contact and grind a work piece.
During this operation, the rotating grindstone moves back and forth in a direction of the feed shaft to coincide with a distance computed by a control device. For computing the distance, a radius of grindstone is used as a calculating parameter. However, if the radius of the grindstone is not specified exactly, errors arise in the form and circularity of the ground work piece (such as a cam and a pin).
A variety of mechanisms to specify the radius of the rotating grindstone have been proposed in prior art references (such as the Japanese Patent Provisional Publication No. 63678 of 1992 and the Japanese Patent Publication No. 47352 of 1993).
An object of the invention is to provide a new method and apparatus to specify a radius of a rotating grindstone, or a device for measuring a radius of grindstone in a grinding machine which exactly measures a radius having a simple structure which does not contact the rotating grindstone.
In order to achieve the above-mentioned object, the present invention is characterized by a device for measuring a radius of grindstone in a grinding machine that numerically controls a feed shaft of a wheel spindle stock. The device comprises a non-contact detector to detect a rotating grindstone on the wheel spindle stock reaching two different fixed positions in a feed direction of said feed shaft, and an arithmetic means to compute a radius of the rotating grindstone from points detected by the non-contact detector. In this case, the grinding machine may numerically control the feed shaft and a main shaft having a work piece fixed thereto synchronously.
According to this invention, the non-contact detector detects the rotating grindstone on the wheel spindle stock reaching two different fixed positions, thereby specifying two positions of the rotating grindstone on the feed shaft. The radius of the rotating grindstone is calculated by the arithmetic means with data related to the two positions of the rotating grindstone and their corresponding non-contact positions.
The non-contact detector is movable toward two different detecting positions to detect the rotating grindstone at each position. According to this mechanism, a single non-contact detector is sufficient to detect the rotating grindstone on the wheel spindle stock reaching two different fixed positions.
Moreover, two non-contact detectors can be provided at different detecting positions to detect the rotating grindstone. According to this mechanism, it is not necessary to move the non-contact detectors to detect the rotating grindstone on the wheel spindle stock reaching two different fixed positions.
Furthermore, the non-contact detector is a laser beam detector having a flood-light for radiating a laser beam and a light-interceptor for receiving it. According to this mechanism, the laser beam is intercepted by the rotating grindstone, thereby preventing the light-interceptor from receiving it. As a result, the position of the rotating grindstone is recognized.